IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication, called WiFi, in the unlicensed (2.4, 3.6, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the WiFi frequency bands. For example, IEEE 802.11ac is a wireless networking standard in the 802.11 family providing high-throughput WLANs on the 5 GHz band. Significant wider channel bandwidths (20 MHz, 40 MHz, 80 MHz, and 160 MHz) were proposed in the IEEE 802.11ac standard. For backward compatibility, a wide bandwidth channel is composed of several narrow bandwidth channels, e.g., a channel of 80 MHz is composed of four 20 MHz channels. Similarly, in WLAN based on IEEE 802.11ah standard, a channel of 8 MHz is composed of four 2 MHz channels by scaling down the IEEE 802.11ac channels by a factor of 10.
In IEEE 802.11ac, a transmitter of a BSS (basis service set) of certain bandwidth is allowed to transmit radio signals onto the shared wireless medium depending on clear channel assessment (CCA) sensing. For a BSS of certain bandwidth, a valid transmission sub-channel shall have bandwidth, allowable in the IEEE 802.11ac, equal to or smaller than the full bandwidth of the BSS and contains the designated primary sub-channel of the BSS. Based on the CCA sensing in the valid transmission bandwidths, the transmitter is allowed to transmit in any of the valid transmission sub-channels as long as the CCA indicates the sub-channel (or full channel) is idle. This dynamic transmission bandwidth scheme allows system bandwidth resource to be efficiently utilized.
An enhanced distributed channel access protocol (EDCA) is used in IEEE 802.11ac as a channel contention procedure for wireless devices to gain access to the shared wireless medium, e.g., to obtain a transmitting opportunity (TXOP) for transmitting radio signals onto the shared wireless medium based on CSMA/CA with random back-off contention scheme. The basic assumption of EDCA is that a packet collision can occur if a device transmits signal under the channel “BUSY” condition when the received signal level is higher than CCA level. On the other hand, a device can transmit signal under the channel “IDLE” condition when the received signal level is lower than CCA level. Typically, the EDCA TXOP is based solely on activity of the primary channel, while the transmit channel width determination is based on the secondary channel CCA during an interval (PIFS) immediately preceding the start of the TXOP.
Specifically, the current channel access method in WLAN based on IEEE 802.11ac is as follows. The primary channel CCA (PC CCA) is always on primary channels (PC). By comparing received signal strength of the PC with pre-determined thresholds, also referred to as CCA levels, PC CCA indicates the PC is “IDLE” or “BUSY”. When the PC is “IDLE”, a counter is starting to count down. When the counting down reaches zero, the station checks the status of secondary channels (SC) in point (coordination function) inter-frame space (PIFS) time period. If the SC is “IDLE” in PIFS time, the station transmits radio signals using wide bandwidth; else, the station transmits radio signals using only the 20 MHz PC.
The problem of such method is that wideband has less opportunity than narrow band because the secondary channels (SC) could be used by neighbor basic service set (BSS). However, wider channel bandwidth transmission is both bandwidth and power efficient. First, in OFDM/OFDMA systems, higher number of subcarriers are achieved with reduced guard tones. Second, lower rate codes are more powerful than higher rate codes. Furthermore, wider channel bandwidth transmission causes less interference in dense deployment environment because the transmitting (TX) spectral density is lower. Due to these reasons, improving the wide bandwidth opportunities can enhance the throughput of the network.